Thread tension device for sewing machines



y 1951 R. E. JOHNSON 2,986,358

THREAD TENSION DEVICE FOR SEWING MACHINES Filed Jan. 27, 1958 IN VENTOR. Ralph E. Johnson 9 ATTORNEY United States Patent THREAD TENSION DEVICE FOR SEWING MACHINES Ralph E. Johnson, Mountainside, NJ., assignor to The Singer Manufacturing Company, Elizabeth, N.J., a corporation of New Jersey Filed Jan. 27, 1958, Ser. No. 711,302

3 Claims. (Cl. 242-150) The present invention relates to a thread tension device for sewing machines and more particularly to a tension -disc for use in such a device.

' The primary object of the present invention is to provide a thread tension device for sewing machines which will produce a more uniform tension on the thread. In accordance with the present invention, this object is obtained by the use of a novel tension disc.

Further objects of this invention are to provide a universal tension disc which can be used in combinations of two or more to accommodate a single or a plurality of needle threads without additional elements, and at the same time, to provide a tension disc which is less expensive to manufacture.

Having in mind the above and other objects that will be evident from an understanding of this disclosure, the invention comprises the devices, combinations and arrangements of parts as illustrated in the presently preferred embodiment of the invention which is hereinafter set forth in such detail as to enable those skilled in the art readily to understand the function, operation, construction and advantages of it when read in conjunction with the accompanying drawing in which:

Fig. 1 is a sectional view of a thread tension device embodying the present invention mounted upon a sewing machine.

Fig. 2 is a perspective view of a tension disc of the device illustrated in Fig. 1.

Fig. 3 is a sectional view of the tension disc of the device illustrated in Fig. 1.

The present invention is herein disclosed as embodied in the needle thread tension device forming the subject matter of my prior application Serial No. 692,323, filed October 25, 1957, now Patent No. 2,955,775. This de-' vice includes a cylindrical arbor I mounted on the frame of the sewing machine, a fragmentary portion of which is illustrated at 2. The inner end of the arbor 1 is provided with a longitudinally grooved enlarged diameter portion 3 about which is coiled one end of a check spring 4 and to which the one end of the check spring is anchored.

The enlarged diameter portion 3 defines a shoulder 5 against which abuts the innermost one of three identical tension discs 6 loosely mounted on the arbor 1. The tension discs 6 are resiliently urged against each other in 'turn and against the shoulder 5 by the usual beehive spring "7 coiled about the arbor 1 and acting at its inner end on the outermost one of the tension discs 6 through an inner spring cover 8 and a guard plate 9. The outer end of the spring 7 abuts against an anchor disc 10 having a diameter bar 11 seated in a slot 12 extending axially inwardly from the free end of the arbor 1 to hold the disc 10 against turning relatively to the arbor 1. 'The disc 10 in turn abuts against an adjusting nut 13 threaded onto the free end of the arbor 1 and has a clamping nut 14 threaded onto it. The inner end of the adjusting nut 13 is provided with a flange 15 against which the web of an outer spring cover 16 is clamped by the nut 14. The outer spring cover 16 is provided with 8. lug

2,986,358 Patented May 30, 1961 2 17 that cooperates with a stop arm 18 in the anchor disc 10 to limit turning of the cover 16 to one revolution.

In the illustrated embodiment of the invention there are three of the tension discs 6 to provide two separate thread paths for two needle threads which are placed individually between the discs 6. In operation, the spring 7 acting at its outer end against the adjusting nut 13 and acting at its inner end through the inner spring cover 8 and guard plate 9, biases the tension discs 6 successively against each other and against the shoulder 5. Turning the adjusting nut 13 will displace the same axially of the arbor 1 to vary the compression of the spring 7 and thus to vary the bias imposed upon the tension discs. The lug 17 on the outer spring cover 16 and the stop arm 13 on the anchor disc 10 limit turning of the adjusting nut 13 to one revolution and thus to a predetermined range of action. To vary the range of action of the tension,

the clamping nut 14 is backed 0E to release the outer spring cover 16 and thus provide for rotation of the cover 16 relatively to the adjusting nut 13.

Each of the tension discs 6 is circular and has a centrally located aperture 19 for receiving the arbor 1. Each of the discs 6 includes a central flange 22, a peripheral flange 23, and an intermediate raised annular portion 20 upon each face thereof. The raised portions 20 of each of the discs are formed concentrically of the apertures 19 and have planar top surfaces or extremities 21 that are disposed in planes perpendicular to the axis of the apertures 19. The surfaces 21 constitute the thread en gaging surfaces of the discs and cooperate with the cor-- responding surface of the adjacent disc to impose a tension upon a thread running between the discs. The discs 6 can be arranged in pairs to accommodate a single thread or can be arranged in combinations of three, as illustrated in the drawings, to accommodate two threads, or further, can be arranged in combinations of more than three to accommodate three or more threads. This construction is in contrast to the prior dished construction as illustrated in my above noted application Serial No. 692,323 in which the tension discs are made with abutting convex surfaces between which the thread runs. In order to provide for two threads with such dished tension discs, it is necessary to provide two pairs of tension discs or else, as illustrated in my prior application, a pair of tension discs and a planar separator disc or spacer between them. With the prior construction it is diflicult to accommodate more than two threads since the necessary accumulation of discs and/or spacers cannot be accommodated on the arbor of a conventional tension device. The elimination of the need for a separate spacer effects substantial economies not only in that the mass production of a single item is much less expensive than the manufacture of a reduced number of two different items, but also in that handling and storage are cheaper and in that it reduces the required stock and inventories.

A further advantage of the present invention over the prior dished construction is that they are simpler to manufacture and at the same time produce a more uniform tension. A uniform tension requires that the abutting surface of each disc be planar. The dished tension discs of the prior art were punched from sheet metal, formed into shape by stamping and then hardened. The stamping operation produces stresses in the piece which during the hardening operation produce warping. To minimize warping, the discs are subjected first to a reverse stamping operation in which they are dished in the opposite direction from that of the fiished disc and are then stamped into the finished shape. Another operation in the manufacture of the present tension discs is lapping the stacked discs. Since the thicknesses of the disc are not uniform, either because of variations in the stock from which they were punched or because of the previous stamping opassesses erations, and because the discs are not bent uniformly and are not uniformly planar; the lapping of one disc with another will not produce identical convex abutting sur- .faces on .-all the discs. ilThe-discsin accordance with the present invention are swaged Yfrom slugs which from the standpoint of avoiding warping gproduces a more :favorable internal structure, and are lapped by parallel grinding wheels. Thus, the-discs areuniform and .theabutting faces are planar and parallel, with the result that they will produce a more uniform tension.

The raised annular portions 20 effect a spacing of the peripheral flanges .23 when the discs are stacked as illustrated in Fig. 1, thus facilitating i-ntroducingathread between the discs. The central flange 22 is made as small as practical to reduce the bearing surface between thedisc andthearbor .1 to a minimum. This construction reduces the likelihood of the thread .being caught between the edge -.of thedisc about'the hole 19 and the arbor 1, and also permits wobbling of the disc relatively to the arbor 1 to accommodate the thread and to provide for alignment of the :discs relatively'to each other.

Having thus described the invention, what Ilclaim herein is:

1. A thread tension disc for-sewing machines comprisinga circular disc that is symmetrical relatively to a plane normal to the axis thereof, said disc havinga thin central flange with a centrally located aperture for mounting the same upon the arbor of asewing machine thread tension device, the aperture being dimensioned relatively to the arbor and to the thickness of the central flange to provide for movement of the disc freely rendwise of the arbor and for wobbling of the discupon the arbor, a raised annular portion upon-each face of said disc and arranged concentrically of said aperture, and parallel planar thread engagingsurfaceson said raised annular portions -and-arranged normal to the-axis ofsaid disc.

2. A thread tension disc inaccordance with claim 1 in which, outward y .of aidliais s aunularpc ticus, than:

is provided a peripheral flange of reduced thickness relatively to said raised annular portion to facilitate placing of a thread between two such discs when juxtaposed with the adjacent thread engaging faces thereof in engage ment.

3. .A hrea tension devi e for sewing m hine omprising an arbor, a plurality .of opposed thread tension discs mounted upon said arbor, and means for resiliently biasing S id tension discs into engagement, :said tension discs comprising :a circular disc that issymmetrical .relatively to a plane normal to the axisthereof, said disc having a thin central flange with acentrally located aperture for mounting the same upon the arbor of a sewing machine thread tension device, the aperture being dimensioned relatively to the arbor and to the thickness of the central flange to provide for movement of the disc freely endwise of the arbor and for wobhling Qf the-.disc upon :the arbor, araised annular portion upon each faee of said disc and arranged concentrically :Qf ;s ai d aperture, and parallelplanar threadengaging surfaces onfiaidraised annular portions and arranged normal to the axis ofsaid disc.

References Cited .in the file of this patent UNITED STATES PATENTS 2093157 "Bradford Oct. 22, 1878 1,198,545 'Hofmann Sept. '19, 1916 1,312,799 ,Motfatt et al. Aug. 12,1919 "2; 189,732 Howell Feb. 6, 11 94.0

FOREIGN PATENTS 1-43'55584 Italy 'May 1-8, 1-948 OTHER REFERENCES Germany, .Ser. No.:St. 8146, printed Oct. 3,1, 3956 l (KL 52a 33112). 

